This invention relates to refrigeration and/or heat pump cycles and more particularly to apparatus for carrying out these cycles.
In theoretical vapor compression refrigeration, saturated vapor refrigerants at low pressure enter a compressor and undergo isentropic compression. The high pressure vapor enters a condenser and heat is rejected from the fluid at constant pressure. The working fluid leaves the condenser as a saturated liquid. An isenthalpic throttling process follows across an expansion valve or capillary tube. The working fluid is then evaporated at constant pressure with the working fluid absorbing heat to complete the cycle.
Direct expansion refrigeration units have not generally taken advantage of the energy or available work lost in the execution of the cycle through the throttling or free expansion of the liquid refrigerant into the evaporator of the refrigeration machine. Generally, only limited use has been made of the conversion into mechanical energy of the kinetic energy possessed by the refrigerant which flows from the high pressure side to the low pressure side of the refrigeration system.
It is known for refrigerant to be expanded in a turbine motor prior to passing into an evaporator, and the turbine motor is used to drive a centrifical refrigerant compressor or perform other work in the system. While such expedients may provide advantages in a refrigeration system, they can not utilize all the energy which would otherwise be a loss in the system, for performing useful work to increase the efficiency of the system.
Several advantages are obtained by the use of positive displacement expansion motors as disclosed herein compared to the prior art. These positive displacement closed expansion motors have a theoretical efficiency of 100 percent compared to about 65 percent for the type of turbine required for the usual refrigeration system.
The closed expansion motor also reduced losses caused by the absence of thermodynamic equilibrium in the more rapid open expansion of a turbine. Further, the basic process of open expansion of a high pressure liquid to produce kinetic energy of the fluid and then conversion of this kinetic energy into mechanical energy in a turbine has inherent losses not encountered in closed expansion inside the expanding chamber of a direct expansion motor. This is specially true for the subject system where two phase flow is involved. Also, the turbine must have a tip speed of the same magnitude as the velocity of the expanded gas (open expansion through nozzle) to operate efficiently. This requires rotation at a high rate or speed which is not compatable with direct coupling to the main refrigeration compressor or a blower, etc., as disclosed here.